For many years, it has been possible to change the shape of the cornea to correct disorders, such as myopia, keratoconus, and hyperopia. In myopia, the dioptric power of the eye is too great; this can be corrected by flattening the cornea. In keratoconus, the cornea has an abnormal cone-shaped projection at its center; it can also be corrected by flattening. Hyperopia can be corrected by increasing the curvature of the cornea to decrease the dioptric power of the eye.
Radial keratotomy is a surgical procedure that can correct myopia by flattening the center portion. Up to sixteen non-penetrating incisions are made in the cornea from near the center outward toward the rim. The internal pressure of the eye causes the cornea to bulge where cuts have been made; the uncut center of the cornea flattens as a result. The side effects of radial keratotomy include perforation of the cornea, glare, and loss of endothelial cells leading to hydration of the cornea.
Because of these drastic side effects, researchers have turned to other techniques for modifying the cornea. One particular approach involves the application of heat to the cornea. Thermal techniques for reshaping the cornea are based on the fact that the cornea stroma shrinks permanently when raised to 55.degree.-58.degree. C. The stroma is the central, thickest layer of the cornea and consists mainly of collagen fibers. If the pattern of shrinkage in the stroma is properly chosen, the resulting stresses can be used to reshape the cornea. The cornea has been flattened to correct keratoconus by applying a heated rod to it (J. V. Aquavella, "Thermokeratoplasty", Opthalmic Surgery, Vol. 5, No. 1, Spring 1974, pp 39-47). Since the rod heats by conduction, the maximum temperature occurs at the cornea surface. Thus, the epithelium --the outer layer--can be destroyed. In another thermal approach, the corneal stroma of excised eyes has been heated by radio-frequency techniques combined with surface cooling (J. D. Doss and J. I. Albillar, "A Technique for the Selective Heating of Corneal Stroma", Contact Lens, Vol. 6, No. 1, Jan.-Mar. 1980, pp 13-17; U.S. Pat. No. 4,326,529 issued 4/27/82 to James D. Doss). This produces a local maximum of temperature below the epithelium. However, the Doss system requires two conductors, or electrodes, between which the RF current flows. One conductor, i.e., the Rear of Head Electrode of FIG. 5, is a groundplane. In practice, it must somehow be located behind the eyeball. Therefore, unless the rear electrode is implanted, RF energy must pass completely through the head with possible damaging consequences to eye tissue or other tissue located behind the cornea.